We remember (perhaps) from our chemistry classes that phosphorus is one of the primary elements. I do not recall how important phosphorus is in the human physiology but in 1896 they really did not understand.
Looking for an obituary in the Spokesman-Review for 14 October 1896 I came upon this teeny little bit: "Phosphorus In The Brain..... The human brain contains a considerable proportion of phosphorus, varying from 1/20th to 1/30th of the whole mass. If the average weight of the brain be taken at 47 and 1/2 ounces it will then count phosphorus as amounting to 1 and 1/2 ounces. Phosphorus is found to be almost entirely wanting in the brains of idiots."
And how, I wonder, did they know that????